Add test confirming json merge behavior

util/pkg/reflectutils/walk.go

@@ -44,6 +44,7 @@ func IsMethodNotFound(err error) bool {
 
 // JSONMergeStruct merges src into dest
 // It uses a JSON marshal & unmarshal, so only fields that are JSON-visible will be copied
+// If both source and destination has a value for a field, source takes presedence
 func JSONMergeStruct(dest, src interface{}) {
 	// Not the most efficient approach, but simple & relatively well defined
 	j, err := json.Marshal(src)

util/pkg/reflectutils/walk_test.go

@@ -0,0 +1,40 @@
+/*
+Copyright 2022 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package reflectutils
+
+import "testing"
+
+type testStruct struct {
+	Value string `json:"value,omitempty"`
+}
+
+func Test_Merge(t *testing.T) {
+	source := testStruct{
+		Value: "foo",
+	}
+
+	destination := testStruct{
+		Value: "bar",
+	}
+
+	JSONMergeStruct(&destination, &source)
+
+	// verify source value overrides destination
+	if destination.Value != "foo" {
+		t.Errorf("unexpected value: %s", destination.Value)
+	}
+}